importance of surface energy considerations for explaining polymorphism at small dimensions. [19] The arguments presented here have demonstrated that the length scale at which a solid-state phase change occurs in pentacene films, given by h c , is related to the ratio of the differences between the (001) surface energies and the bulk energies for the two distinct phases. ExperimentalPentacene powder as received from Aldrich was thermally evaporated from a tungsten wire basket onto room-temperature amorphous carbon coated mica substrates under a vacuum of~10 ±5 torr. Films approximately 20 nm in thickness were evaporated at a rate of approximately 1 nm s ±1 . The pentacene films on amorphous carbon were then floated off the mica onto deionized water for collection with copper grids. Low voltage electron microscopy [20] was done on a LVEM5 from Delong Instruments operating in transmission mode at 4.7 kV. HREM was performed on a 400 kV JEOL 4000 EX operating under low dose conditions [21]. The end-point electron dose for destruction of crystallinity in pentacene was determined to be 0.25 ± 0.05 C cm ±2 at 400 kV [22]. Electron diffraction patterns were taken with a dose of 10 ±4 to 10 ±3 C cm ±2 . HREM images were taken with a dose of less than 0.09 C cm ±2 . Typical HREM images were taken at a magnification of 60 000 , a screen current density of 15 pA cm ±2 and an exposure time of 1.4 s. Negatives were digitized using an Imacon Flextight scanner with 5760 dpi resolution. The Cerius 2 v. 4.6 software package from Accelrys was used for modeling of the pentacene structure and simulation of ED patterns. The Dreiding 2.21 force field [17] was used to describe inter-and intramolecular interactions with a Buckingham exponential-6 potential and a simple harmonic oscillator, respectively. The triclinic pentacene lattice parameters and atomic coordinates were directly entered from the experimentally determined crystal structure [11].

Therapeutic systems to induce reactive oxygen species (ROS) have received tremendous success in the research of tumor theranostics, but suffered daunting challenges in limited efficacy originating from low presence of reactants and reaction kinetics within cancer cells. Here, ferrous sulfide‐embedded bovine serum albumin (FeS@BSA) nanoclusters, in an amorphous nature, are designed and synthesized via a self‐assembly approach. In acidic conditions, the nanoclusters degrade and simultaneously release H2S gas and Fe2+ ions. The in vitro study using Huh7 cancer cells reveals that Fe2+ released from FeS@BSA nanoclusters induces the toxic hydroxyl radical (·OH) effectively via the Fenton reaction. More interestingly, H2S gas released intracellularly presents the specific suppression effect to catalase activity of cancer cells, resulting in the promoted presence of H2O2 that facilitates the Fenton reaction of Fe2+ and consequently promotes ROS induction within the cells remarkably. After intravenous administration, the nanoclusters accumulate in the tumors of mice via the enhanced permeability and retention effect and present strong magnetic resonance imaging (MRI) signals. The findings confirm this therapeutic system can enable superior anti‐tumor performance with MRI guidance and negligible side effects. This study, therefore, offers an alternative gas‐amplified ROS‐based therapeutic platform for synergetic tumor treatment.

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Room-temperature ferromagnetism has been observed in Fe-doped PbTiO3 nanocrystals. The magnetism of the nanocrystals develops from diamagnetism to ferromagnetism and the paramagnetism on increasing nominal Fe doping concentration from 0to4mol%. Transmission electron microscope (TEM) and high-resolution TEM data indicate that Fe-doped PbTiO3 nanocrystals with the size of ∼100nm are organized to form a planarlike self-assembly via oriented aggregation. These assembled nanostructures effectively improve room-temperature ferromagnetism of the sample. The exchange interaction of ferric ions via an electron trapped in a bridging oxygen vacancy (F center) is employed to explain the ferromagnetism of Fe-doped PbTiO3 nanocrystals.

Topological structures based on controllable ferroelectric or ferromagnetic domain configurations offer the opportunity to develop microelectronic devices such as high-density memories. Despite the increasing experimental and theoretical insights into various domain structures (such as polar spirals, polar wave, polar vortex) over the past decade, manipulating the topological transformations of polar structures and comprehensively understanding its underlying mechanism remains lacking. By conducting an in-situ non-contact bias technique, here we systematically investigate the real-time topological transformations of polar structures in PbTiO3/SrTiO3 multilayers at an atomic level. The procedure of vortex pair splitting and the transformation from polar vortex to polar wave and out-of-plane polarization are observed step by step. Furthermore, the redistribution of charge in various topological structures has been demonstrated under an external bias. This provides new insights for the symbiosis of polar and charge and offers an opportunity for a new generation of microelectronic devices.